Even though radiation therapy often achieves a cure or long term remission of cancer, the treatment process and the adverse effects which accompany it can cause physical and psychological stress. Previous nursing and psychological research on coping with stressful health care procedures suggest that the stress of radiation therapy could be influenced by reducing uncertainity about specific aspects of impending experiences. Uncertainty about the experience can be reduced by information that assists patients in predicting the sensations and symptoms they will experience and when those sensations and symptoms will occur and how long they will last. Preparatory information consisting of that content is expected to increase cancer patients ability to tolerate the stress of treatment and maintain, or regain, functional status during and following radiation therapy. That hypothesis will be tested using an experimental design with random assignment of patients. The experimental research will begin with prostate cancer patients. The indicator of disruption of customary life activities will be the Sickness Impact Profile. Emotional states will be assessed with the Profile of Mood States. The experimental interventions will focus on four phases of the radiation therapy experience; a) treatment planning, b) first treatment, c) development of side effects, and d) following treatment termination. Data from outcome indicators will be collected during and three months following treatment. Research to document the experience of receiving radiation therapy from the patient's perspective, with patients who have cancer in sites other than the prostate gland, will continue. That research is essential to determining the content of the interventions when extending the experimental research to patients with cancer in other sites. The research can contribute to a scientific rationale for and the specific content of effective preparatory interventions provided patients in radiation therapy departments.